1. Field of the Invention
The present invention relates to an ink-jet recording head and an ink-jet recording device wherein a piezoelectric element is formed in a part of a pressure generating chamber communicating with a nozzle aperture for jetting an ink droplet via a diaphragm so that an ink droplet is jetted by the displacement of the piezoelectric element.
2. Description of the Related Art
For an ink-jet recording head wherein a part of a pressure generating chamber communicating with a nozzle aperture for jetting an ink droplet is constituted by a diaphragm and an ink droplet is jetted from the nozzle aperture by deforming the diaphragm by a piezoelectric element and pressurizing ink in the pressure generating chamber, two types are used, such as a piezoelectric actuator in a longitudinal vibration mode for extending or contracting a piezoelectric element axially, and a piezoelectric actuator in a flexural vibration mode are used.
For the former, the volume of a pressure generating chamber can be varied by touching the end face of a piezoelectric element to a diaphragm and a head suitable for high density printing can be manufactured. However, on the other hand, there is a problem that a difficult process for cutting a piezoelectric element in the form of the tooth of a comb in accordance with the arrangement pitch of nozzle apertures, and work for positioning and fixing the cut piezoelectric element over a pressure generating chamber are required, and its manufacturing process is complicated.
In the meantime, for the latter, a piezoelectric element can be fixed on a diaphragm in a relatively simple process by sticking a green sheet which is a piezoelectric material in accordance with the shape of a pressure generating chamber and burning it. However, on the other hand, there is a problem that area to some extent is required because flexural vibration is utilized and a high density arrangement is difficult.
In the meantime, to solve the problem of the recording head equivalent to the latter, as disclosed in Japanese published unexamined patent application No. Hei 5-286131, a recording head wherein a piezoelectric element is independently formed for every pressure generating chamber by forming a uniform piezoelectric material layer on the whole surface of a diaphragm by a thin film technique and cutting the piezoelectric material layer in a shape corresponding to each pressure generating chamber by lithography, is proposed.
Accordingly, there is an advantage that work for sticking a piezoelectric element on a diaphragm is not required, and not only a piezoelectric element can be fixed by a precise and convenient method such as lithography, but the piezoelectric element can be thinned and high speed driving is enabled.
In this case, a piezoelectric element corresponding to each pressure generating chamber can be driven by providing at least only an upper electrode for every pressure generating chamber with a piezoelectric material layer provided on the whole surface of a diaphragm. However, it is desirable because of a problem of the quantity of displacement per unit driving voltage and stress upon a piezoelectric layer in a part across a part opposite to a pressure generating chamber and the outside, that a part except at least one end of a piezoelectric layer and an upper electrode respectively constituting a piezoelectric element is not continuously extended outside a pressure generating chamber. However, there is a problem that in such a structure, a crack is readily made in a piezoelectric layer particularly crossing a boundary.
If a substantial driving part of a piezoelectric element is provided apart from over a peripheral wall and corresponding to each pressure generating chamber, structure wherein a piezoelectric element corresponding to each pressure generating chamber is generally covered with an insulating layer, a window (hereinafter called a contact hole) for forming a connection to a lead electrode for supplying voltage for driving each piezoelectric element is provided to the insulating layer corresponding to each pressure generating chamber and the connection of each piezoelectric element and a lead electrode is formed in a contact hole, is proposed. However, the above structure has as a problem that stress is concentrated in the vicinity of a contact hole and breaking and, other problems are readily caused.
For the above ink-jet recording head, to enhance the efficiency of the displacement of a diaphragm by the driving of a piezoelectric element, a structure in which a diaphragm in a part corresponding to both sides of a piezoelectric element is thinned, is proposed. However, when displacement is increased as described above, the above problem is promoted. Further, there is also a problem that breaking such as a crack is readily caused in the vicinity of the peripheral wall of a pressure generating chamber of a diaphragm or in the vicinity of a contact hole.
These problems are readily caused particularly in the case where a piezoelectric material layer is formed by a film forming technique. The reason is that as a piezoelectric material layer formed by film forming technique is very thin, its rigidity is lower, compared with a piezoelectric material layer on which a piezoelectric element is stuck.